Method for dewaxing oils



Jan. 29, 1935. E. W.YGARD l ,989,3 5

METHOD FOR DEWAXING OILS Filed Aug. 21, 1935 I N VEN TOR Ear/e W Gard B Y I ATTORNEY.

Patented Jan. 29, 1935 METHOD FOR DEW-AXING oms Earle W. Gard, Palos Verdes-Estates, Calif., as-

signor to Union Oil Company, of California, Los Angeles, Calif., a corporation of California Application August 21, r933, Serial No. 686,016

a Claims. (p1. lee-19') The present invention relates to a process for separationof waxes. For example, the use of a the separation from petroleum of those hydrocarbons which are normally solid at ordinary temperatures. In accordance with this process, I am able to separate from petroleum or mineral oil such substances as paraffin, crystalline or amorphous wax or gummy or resinous substances which may be present. -While the invention is particularly adapted to the removal of paraflin, amorphous or crystalline wax or gummy or res inous substances from petroleum residues to pro duce lubricating oil, it may be utilized in the treatment of any other petroleum fractions where it is desirable to separate the oil from the foregoing substances.

Many crude oils from which lubricating oil is produced contain paraffin or wax. It is ,found associated with lubricating oil fractions of paraffin base crude oil and also with lubricating oil fractions produced form'any of the mixed base and asphalt base crude oils. The presence of wax in lubricating oil is not only of doubtful value but also limits the temperature at which lubricants containing it may be used because of congelation at low temperatures. Therefore, in the production of lubricating oils from petroleum fractions containing wax or paraffin, it is customary to remove a substantial portion of the wax or paraflin present in the oil in order to lower the temperature at which the lubricant congeals. The temperature at which an oil congeals is commonly referred to as its pour point and this value is usually obtained according to Method D--9730 outlined by the American Society of Testing Materials.

One of the more successful processes suggested for the production of lubricating oil from petroleum fractions or residues which contain substances congealing at low temperatures as set forth above and to which I shall hereinafter. refer as wax, consists in first diluting the .wax containing oil with a light hydrocarbon solvent such as one which is vaporous at normal temperatures and pressures as, for example, propane, under a pressure suflicient to maintain the solvent in its liquid state and subsequently chilling .the solution to effect percipitation of the wax. This mixture is subjected to-settling, centrifuging or filtration for the purpose of removing the precipitated wax from the solution of oil and solvent. The oil solvent solution is then heated to vaporize the solvent from the oil.

The present invention relates to an improvement on the aforesaid process which has several advantages over other known processes for the light diluent such as propane, lowers the viscosity ,of the. chilled mass sufllciently to facilitate the separation ofthe precipitated wax from the f chilledsolutionof propane and oil. Another advantage of using this type of solvent as a diluent for the oil containing wax is that by allowing a portion of.the solvent to vaporize under re- ;duced pressure, the necessary refrigeration is obtainedto chill the oil to the desired dewaxing temperature. 'The waxy oil is first dissolved under pressure, in the light liquid hydrocarbon and then abortion of the light liquid hydrocarbon is vaporizedior allowed to boil off at reduced pressure which thereby lowers the temperature of the waxy oil dissolved in the remaining solvent to a point sufliciently low to precipitate the wax. Thus, the light liquid hydrocarbon functions both as a diluent for the wax bearing oil and also as an internal refrigerant to chill the solution of oil and wax to the proper dewaxing temperature. Furthermore, this'internal refrigeration may occur in the propane itself prior to its intermixture with the oil and wax.

The objection to the foregoing process has been that unless extremely long settling periods are provided, a portion of the wax is carried over with the oil solvent. solution decanted from the wax settling chamber. I have observed in the foregoing process that a portion of the wax precipitated, that is, released from solution by refrigeration, settles rapidly and in a relatively short time, while the remaining portion of the wax remains in a cloudy suspension in the solution of solvent and oil and requires considerable time to settle. This is due to the different physical characteristics of the two types of wax. The first portion of the wax which settles rapidly to the bottom of the settler or decanter is a hard, heavy'and solid wax. It is granular and crystalline and has a larger particle size than the remaining wax in suspension. The remaining portion of the wax is soft and slime-like and is in so fine a form of subdivision that filtering or settling is substantially impeded. This type of wax is in the nature gregation which are formed during the chilling operation will not readily settle out by cold settling even in the presence of propane which increases the difference in specific gravity between the solution of ofl in the solvent and wax.

Thus, after a certain time of settling, there appears to be three distinct stratified layers, the first comprises the hard granular wax which settles rapidly to the bottom of the settler. Superimposed on this layer is a strata of oil and solvent containing the finely divided wax in suspension and above this is a clear solution of oil and solvent substantially free from either type of wax. In

decanting the supernatant solution of oil and solvent substantially free from wax, there is a tendency for the middle layer containing the fine wax in suspension to be carried over with the oil solvent solution. The present process is aimed at the prevention of this occurrence. I have discovered that if a portion of the middle layer of oil solvent solution containing the finely divided wax in suspension is continuously withdrawn from the settling chamber, the tendency for the finely divided wax to be carried into the upper strata and thus decanted with the clear oil solvent solution is obviated. If the withdrawn portion is passed to the stream of oil entering the treating process and commingled therewith, the wax will also be commingled with the naturally occurring wax of the oil stream and will re-precipitate in the subsequent chilling of the oil solvent solution. When the chilled mixture is again passed into the settler, there will be present a larger proportion of wax so that a considerably larger amount of the'wax will settle to the bottom rapidsince the amount of wax settling rapidly to the bottom of the decanter is dependent upon the percent of wax in the mixture and the manner in which it was precipitated from solution. By the latter statement is meant that by shock chilling or rapid cooling of the solution of oil, wax and propane, a large proportion of the wax will precipitate in a form too finely divided for chi-- cient settling and/or filtration. If the solution is cooled or chilled slowly to the final low temperature, sufllcient time is allowed to permit the wax crystals to recrystallize and grow, the crystals formed in the earlier stage of cooling at the highperature of approximately -40 er temperature, that is, before" the final low tem- F. is reached, form nuclei for the further development of crystals in the later stage of cooling to lower temperatures. I prefer to include this type of cooling in combination with other features of my invention, although I do not necessarily desire to be limited thereby. However, no matter how slowly the mixture of oil, wax and'propane is cooled, there is inevitably a portion of the wax which remains in suspension in finely divided form and which requires considerable time to settle. This portion of the. wax remains in the 4 middle strata in suspension and when the oil solvent solution is decanted from the settler a portion of the finely divided wax is carried over with the oil solvent solution and thus the pour point of the lubricating oil is increased to a certain extent.

The precipitation of the mixture of oil and added wax will cause more of the finely divided wax to precipitate as. such due. to the added amount but the higher concentration of this finely divided wax will tend towards the agglomeration into larger particles which will then more readily settle to the bottom of the settler.

From the above discussion, it-is apparent that the present invention comprises, in part, a conthe inlet of the charge of chilled oil, solvent and wax and commingling with the withdrawn mixture with the oilentering the process and subsequently chilling the mixture of oil and added wax to precipitate both the wax present in the oil and that added thereto.

When the term light liquid hydrocarbon? is employed herein, I intend to include those hydrocarbons which are normally in the vapor state at atmospheric temperature and pressure. Such hydrocarbons include methane, ethane, propane, iso-butane, butane and mixtures thereof. These may be obtained by rectification of casinghead gasoline by the so-called stabilizing method. They are the overhead thus obtained. They are liquefied by compression and cooling in the conventional manner and are drawn ofi into pressure chambers where they are maintained in the liquid state until they are used. A typical analysis of such a fraction is 6.72% ethane, 72.2% propane, 19.91% iso-butane and 1.17% normal butane. It will be understood, however, that this merely illustrates the type of fraction which and that the composition may vary. Since the preponderant member of this fraction is propane, I will refer to this fraction as propane" or liquid propane for purposes of simplicity.

With the above discussion in mind, it will be perceived that it is a further object of my invention to provide a process for the separation of wax from oil in the production of lubricating oil may be used wherein the oil is mixed with -a hydrocarbon solvent and the mixture chilled to precipitate wax. The chilled mixture is allowed to settle so as to permit wax to settle and a portion of the solution containing wax above the bottom outlet of the settler is withdrawn and returned to the oil enteringthe process.

It is an object of my invention to prevent the carying over of finely divided. wax with oil in the decantation of a settled solution of oil, solvent and precipitated wax by continuously or intermittently withdrawing a portion of the solution of oil and solvent containing finely divided wax from the settling chamber at a point above the strata of more readily settling wax.

Referring to the drawing, a wax or an asphalt 5 and wax containing oil such as a residuum obtained from topping of a Santa Fe Springs crude oil to such extent as to'lave fractions in the residue having a viscosity of 400 to 500 seconds Saybolt Universal at F.'is taken from tank -1 and is withdrawn into line 2 by pump 3 passed into line 4 where it meets a stream of liquefied normally gaseous hydrocarbon solvent such as liquid propane taken from storage tank 5 via line 6 and pump 7 which forces the liquid propane through valve 8 into line 4. The amount of propane introduced into'line 4 will depend upon the character of the oil and the temperatures desired in the chilling column 46 and also upon the amount of solvent desired in the settling chamber 55.

mixed with the oil should be sufficient to effectthe desired chilling temperature by evaporation .eral, an initial volumetric ratio of approximately '7 to volumes of solventto 1 volume of oil will be suflicient to efiect'the desired lowering of temperature and to provide for efiieient settling. However, a lower volumetric ratio may be employed, that is, merely suflicient to effect the desired reduction in temperature and then the mass may be supplemented with further quantities of solvent to bring the ratio up to 4 to 1 in the settling operation. The mixture of liquid propane and oil contain ing asphalt and wax is passed through turbulence or mixing coil 10 into a decanter or asphalt precipitator 11 where the oil containing asphalt is precipitated and settles rapidly as a slurry of substantially pure bitumen or hard asphalt containing some oil and propane. The amount of'propane introduced into the oil will also depend upon whether the oil contain's asphalt or not. If it contains asphalt and it is desired to remove the asphalt at the bottom of the decanter 11 as a slurry of asphalt and propane, that is, as a mixture. of substantially pure bitumen or hard asphalt and propane or as a liquid fraction of an asphalt containing propane and some oil and thus leave a portion of the asphalt in the oil solvent solution to act as nuclear bodies for the wax in the subsequent precipitation of wax by chilling. If it is desired to separate the asphalt as a liquid fraction, the volumetric ratio of propane to oil will be within a range of 0.6 to 6 to 1 depending uponthe character of the oil and the degree to which it was topped. Higher volumetric ratios will precipitate the asphalt as a slurry of substantially pure bitumen and propane. It is preferable to remove as much of the asphalt present in the oil as possible in the decanter 11 and, therefore, it is necessary to employ high volumetric ratios in general from '7 to 10 volumes of propane to 1 volume of oil to accomplish this effect. A pressure of approximately 125 to 175 pounds per square inch gauge and a temperature of about 70 F. to 80 F. is maintained in the decanter or asphalt precipitator 11. The pressure in decanter 11 is controlled by means of equilibruim line 12 controlled by valve 14 and connected to the high pressure propane storage tank 5.

The asphalt precipitated in decanter 11 is withdrawn via line 15 controlled by valve 16 and is forced by pump 17 under pressure through heating coil 18 where it is heated to a sufliciently high temperature to melt the asphalt and vaporize residual propane. The heated mixture is then passed through line 19 and flashed to pressure reduction valve 20 into evaporator 21 which is operated at-a lower pressure. Evaporator 21 is provided with mist extractor 22 and with a perforated pipe 23 controlled by valve 23 through which superheated steam is introduced to supply additional heat and to reduce the asphalt to the proper specification, generally, only as regards flash and fire points. The overhead from evaporator 21 passing through extractor 22 is sent through line 24 controlled by valve 24' to cooler 25 and then via line 26 to separator 2'7. The uncondensed propane from separator 27 is sentv and is then sent via line 32 to cooler 33 where it is liquefied and then" runs down via line 34 into propane storage tank 5. Any condensed light oil in separotor 2'7 is withdrawn through line 35- and condensed water: through line 36. The asphalt is taken from the bottom of evaporator 1'7 and sent through line 38, controlled by valve 39 and pumped by pump 40 into storage tank 41.

The overfiow' from decanter 11 consisting of propane and oil free from asphalt but containing the wax in solution is sent through line 43 by pump 44 through pressure reduction valve 45 into decanter or chilling column 46. In chiller 46, suflicient propane' is permitted to vaporize to reduce the temperature of the remaining material to a sufliciently low temperature which causes wax to precipitate from solution. It is preferable to gradually lower the temperature to a dewaxing temperature and to avoid shock chilling. The

preferable rate of temperature reduction should not exceed 4 F. per minute. The temperature reduction is efi'ected by gradually reducing the pressure in the column 46 by the proper operation of valve 48 on line 4'7 and compressor 31 which is connected to the column by lines 4'7, 49 and 30. The pressure will be gradually lowered to about 0 to 25 pounds gauge which'corresponds to a temperature of approximately -40 F. to 0 F. The propane evaporating in column 46 is passed out of the top through line 4'lcontrolled by valve 48 and then passes into lines 49 and 30 to the suction of compressor 31 where the vapors are compressed, liquefied in cooler 33 and passed to storage tank 5.

Due to the fact that suflicient time must be given to gradually chill the oil and solvent and passing into the chiller 46 and to make the process continuous a plurality of chilling columns like that shown at 46 may .be provided and separated alternately. However, in batch operation merely one of such chilling columns will be sufiicient. In such case, the entire material from decanter 11 may be transferred into column 46 and the chilling accomplished-by controlling the operation of valve 48 on line 47.

The. chilled charge in column 46 comprising oil, propane and precipitated wax is withdrawn from the bottom via line 51 controlled by valve 52 and pumped by pump 53 via line 54 into a settling device 55. In settler 55 a portion of the precipitated wax settles rapidly to the bottom of the settler, while the more fiocculent, light and finely divided wax will require-considerable longer time to settle. It is preferable that the introduction of the mixture via line 54 into the settler be at a point at or above the point where the fine wax remains in suspension in the mixture. This will prevent the fine wax from being carried over with the oil.

The fine wax in suspension is withdrawn from the settler 55 at a point below the inlet 54 as a mixture of wax, propane and oil. This mixture is withdrawn via either of lines 56 controlled by valves 57 and pumped by pump 58 into line 59 by closing valve 60 and opening valve 61 on line 62 and is then passed through heater 63 where it isheated to. approximately atmospheric temperature or higher to melt the wax and passed via line 64 into line 65. If desired, a portion of the mixture may be'by-passed through heater 63 and the remaining portion passed through valve 60 and the mixture commingled in line 65. The

admixture of the heated portion with the unheated portion passed through valve 60 will bring the mixture to the proper temperature for admixture with the incoming oil. It is preferable to continuously withdraw the solution containing the fine wax via line 56 so that an equilibrium is maintained in the settler 55 and thus prevent the passage of the fine wax from being carried over into the oil-propane phase.

The precipitated wax at the bottom of settler 55 is withdrawn by means of gear pump 67 and passed into line 68 controlled by valve 69 and then through heater '10 where it is heated to a temperature suflicient to melt the wax and vaporize residual propane. The heated mixture is then passed via line 71 into separator '72 where vaporized propane is removed by line 73 controlled by valve 74, cooled in cooler 75 and passed via line 76 into line 30 to the suction of compressor 31 where its pressure is raised, condensed in cooler 33 and then passed into propane storage tank 5. The wax is withdrawn from the bottom of separator '72 via line 77 controlled by valve 78 and pumped by pump. 79 into storoge tank 80.

The overflow from settler 55 free from wax is withdrawn via line 81 and pumped by pump 82 through valve 83 into heater 84 provided with mist extractor 85 where the propane present in the oil is vaporized by the aid of steam circulated through closed steam coil 86. The vaporized propane passes out of the heater through line 87, controlled by valve 88, cooled in cooler 89 and then passes through lines 90, 49 and 30 to compressor 31 then through cooler 33 into propane storage tank 5. The dewaxed propane-free oil passes from the heater 84 by means of line 91, controlled by valve 92 and pumped by pump 93 through line 94 into storage tank 95. This oil may be subjected to the conventional acid treatment followed by neutralization and water washing. If desired, the solution of oil and propane removed from decanter 11 may be acid treated and neutralized prior to separation of the wax, or the solution of propane and oil free from wax withdrawn from the settler 55 may be likewise t eated prior to the separation of the residual propane.

It is to be understood that the above ismerely illustrative of preferred embodiments of my in vention of which many variations may be made by those skilled in the art without departing from the spirit thereof.

I claim:

1. A process for dewaxing oil which comprises mixing said oil containing wax with a hydrocarbon diluent, chilling said oil solvent solution to precipitate wax comprising a mixture of more readily settling wax and less readily settling wax, settling the cooled mixture to eilect separation of precipitated wax, withdrawing oil solvent solution substantially free from precipitated wax from the upper part of the settling zone, withdrawing settled wax from the lower part of said zone and withdrawing oil solvent solution containing unsettled wax from a point intermediate said upper and lower parts of the settling zone.

2. A process as in claim 1 in which the with drawn oil solvent solution containing unsettled wax is returned to the oil to be dewaxed.

3. A process for dewaxing oil which comprises mixing said oil containing wax with a liquefied normally gaseous hydrocarbon solvent, chilling said oil solvent solution to precipitate wax comprising a mixture of more readily settling wax and less readily settling wax, separating the readily settling wax from the less readily settling wax by diflerence in specific gravity, and returning the less readily settling wax to the oil to be dewaxed.

4. A process for .dewaxing oil which comprises mixing said oil containing wax with a liquefied normally gaseous hydrocarbon solvent, chilling said oil solventsolution to precipitate said wax, said precipitated wax comprising a mixture of more readily settling wax and less readily settling wax, passing said 011 solvent solution containing said precipitated wax into a settling chamber, settling said precipitated wax from said oil solvent solution in said settling chamber to permit said more readily settling wax to settle at the bottom of said settling chamber and to permit said less readily settling wax to remain in suspension in said 011 solvent solution above said more readily settling wax, and continuously removing oil solvent solution containing said less readily settling wax from said settling chamber during said settling.

5. A process as in claim 4 in which the withdrawn oil solvent solution containing unsettled wax from the point intermediate the upper and lower parts of the settling zone is returned to the oil to be dewaxed.

6. A process for dewaxing oil which comprises mixing said oil containing wax with a liquefied normally gaseous hydrocarbon solvent, chilling said oil solvent solution to precipitate said wax,

said precipitated wax comprising a mixture of more readily settling wax and less readily settling wax, passing said oil solvent solution containing said precipitated wax into a settling chamber stratifying said oil solvent solution containing precipitated wax in said settling chamber into three layers, an upper layer of oil and solvent substantially free from wax, a lower layer of the more readily settling wax, and an intermediate layer of oil and solvent containing said less readily settling wax, withdrawing said upper layer of oil and solvent from said settling chamber, and

withdrawing said intermediate layer of oil and solvent containing said less readily settling wax from said settling chamber, whereby said less readily settling wax is prevented from passing into said layer of oil and solvent during said withdrawal of said upper layer of oil and solvent.

7. A process for dewaxing oil which comprises passing a stream of oil containing wax into a mixing chamber, mixing said oil with a liquefied normally gaseous hydrocarbon solvent in said mixing chamber, chilling said oil solvent solution to precipitate said wax, said precipitated wax comprising a mixture of more readily settling wax and less readily settling wax, passing said 011 solvent solution containing said precipitated wax into a settling chamber, stratifying said oil solvent solution in said settling chamber into three layers, an upper layer of oil and solvent substantially free from wax, a lower layer of the more readily settling wax, and an intermediate layer of oil and solvent containing said less readily settling wax, withdrawing said upper layer or oil and solvent from said settling chamber, withdrawing said intermediate layer of oil and solvent containing said less readily settling wax from said settling chamber and returning said intermediate layer to said oil passing into said mixing chamber.

8. A process for dewaxing oil which comprises passing a stream 01' oil containing wax into a mixer, commingling said 011 in said mixer with a normally gaseous hydrocarbon solvent, chilling said oil solvent solution to precipitate wax, said precipitated wax comprising a mixture of granular and more readily settling wax, and finely divided and more readily settling wax, passing said oil solvent solution containing said precipitated wax into a settling chamber, and in said settling chamber concentrating said finely divided wax in said oil solvent solution as an intermediate layer between a bottom layer of more readily settling wax and an upper layer of oil and solvent substantially free from wax, decanting said upper layer of oil and solvent from said settling chamber, and continuously withdrawing said concentrated intermediate layer of oil and solvent and;

finely divided wax from said settling chamber, whereby said finely divided wax is prevented from passing into said upper layer of oil and solvent during said settling and withdrawal of said upper layer of oil and solvent. 9. A process as in claim -1 in which the withdrawn oil solvent solution containing unettled wax is heated and returned to the oil to be dewaxed. v

10. A process as in claim 3 in which the less readily settling wax returned to the oil to be dewaxed is first heated.

'EARLE W.GARD.

CERTIFICATE OF CORRECTION.

Patent No. 1,989,355. January 29, 1935.

EARLE w. GAR Dr It is hereby certiiied that error appears in the printed specification of the above numbered patent requiring correction as follows: Page 1, first column,

line 20, for "form" read from; page 4, second column,line 49, claim 6, before "layer" insert the word upper; and page 5, second column, line 8, claim 9, for

- f'unettled" read unsettled; and that the said Letters Patent should be read with these corrections therein that the same may conform to the record of the case in the Patent Office.

' Signed and sealed this 26th day of March, A. D, 1935.

Les l ie Frazer (Seal) Acting Commissioner of Patents. 

